# std::linear_congruential_engine<UIntType,a,c,m>::linear_congruential_engine

From cppreference.com
< cpp‎ | numeric‎ | random‎ | linear congruential engine

linear_congruential_engine() : linear_congruential_engine(default_seed) {} | (1) | (since C++11)
explicit linear_congruential_engine( result_type value ); | (2) | (since C++11)
template< class SeedSeq > explicit linear_congruential_engine( SeedSeq& seq ); | (3) | (since C++11)
linear_congruential_engine( const linear_congruential_engine& other ); | (4) | (since C++11) (implicitly declared)

Constructs the pseudo-random number engine.

1) The default constructor.

- If the default-constructed engine is of type `std::minstd_rand0`, the 10000th consecutive invocation of it produces the value 1043618065.
- If the default-constructed engine is of type `std::minstd_rand`, the 10000th consecutive invocation of it produces the value 399268537.

2) Constructs the engine with a seed value value. The engine's initial state is determined as follows:

- If c % m == 0 and value % m == 0 are both true, the state is 1.
- Otherwise, the state is value % m.

3) Constructs the engine with a seed sequence seq. Given std::size_t(std::log2(m) / 32) + 1 as k, the engine's initial state is determined as follows:

1. Creates an invented array object a of length k + 3.
2. Calls seq.generate(a + 0, a + k + 3).
3. Let S be \(\scriptsize (\sum^{k-1}_{j=0} a_{j+3} \cdot 2^{32j}) \mod m \)(∑k-1
   j=0 aj+3·232j
   ) mod m.
4. If both c % m == 0 and S == 0 are true, sets the engine's state to 1. Otherwise, sets the engine’s state to S.

This overload participates in overload resolution only if `SeedSeq` meets the requirements of SeedSequence.
4) The copy constructor. Upon construction, *this == other is true.

### Parameters

value | - | seed value to use in the initialization of the internal state
seq | - | seed sequence to use in the initialization of the internal state

### Complexity

1,2) Constant.
3) Same as the complexity of the `seq.generate` call.
4) Constant.

### Exceptions

3) If `SeedSeq` is not std::seed_seq, throws the exceptions thrown by the `seq.generate` call.

### Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---
LWG 2181 | C++11 | overload (3) would not throw even if the `seq.generate` call throws | propagates the exception
P0935R0 | C++11 | the default constructor was explicit | made implicit

### See also

seed | sets the current state of the engine (public member function)

Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/numeric/random/linear_congruential_engine/linear_congruential_engine&oldid=177249"